Re: [PATCH V2 3/4] arm64/mm: Consolidate page fault information capture

[Mark Rutland <mark.rutland@arm.com>]

On Tue, Jun 04, 2019 at 03:42:09PM +0100, Catalin Marinas wrote:
> On Mon, Jun 03, 2019 at 12:11:24PM +0530, Anshuman Khandual wrote:
> > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> > index da02678..4bb65f3 100644
> > --- a/arch/arm64/mm/fault.c
> > +++ b/arch/arm64/mm/fault.c
> > @@ -435,6 +435,14 @@ static bool is_el0_instruction_abort(unsigned int esr)
> >  	return ESR_ELx_EC(esr) == ESR_ELx_EC_IABT_LOW;
> >  }
> >  
> > +/*
> > + * This is applicable only for EL0 write aborts.
> > + */
> > +static bool is_el0_write_abort(unsigned int esr)
> > +{
> > +	return (esr & ESR_ELx_WNR) && !(esr & ESR_ELx_CM);
> > +}
> 
> What makes this EL0 only?

It returns false for EL1 faults caused by DC IVAC, where write
permission is required. EL0 can only issue maintenance that requires
read permission.

For whatever reason, the architecture says that WnR is always 1b1, even
if read permission was sufficient.

How about:

/*
 * Note: not valid for EL1 DC IVAC, but we never use that such that it
 * should fault.
 */
static bool is_write_abort(unsigned int esr)
{
	return (esr & ESR_ELx_WNR) && !(esr & ESR_ELx_CM);
}

... which would also address your concern about EL1 writes to a user
mapping.

Thanks,
Mark.